Climatology and Aviation Weather Services
Climatology examines average and extreme weather over time and the seasonal patterns that affect flight planning. Candidates should know the global circulation: Hadley, Ferrel and Polar cells; the trade winds, westerlies and polar easterlies; the ITCZ and subtropical highs; and the semi-permanent pressure centres (Azores, Siberian, Icelandic, Aleutian). The jet streams - polar front and subtropical - meander with Rossby waves and steer depressions; their location shifts seasonally.
Regional and seasonal effects
In India the monsoon dominates, with pre-monsoon thunderstorms and dust storms, the southwest monsoon from June to September and the northeast monsoon from October to December. Local effects include sea breezes (strongest in the afternoon), mountain and valley winds, anabatic and katabatic flows, and the mountain wave hazard on the lee of ridges. Föhn-type winds and low-level jets affect particular regions.
Aviation weather services
Services include the world area forecast system, regional area forecasts, aerodrome forecasts, warnings and advisories, and the briefing and flight documentation provided by the meteorological office. Pilots must know the validity periods, issue times and how to obtain pre-flight and in-flight updates. Volcanic ash advisories and tropical cyclone warnings are part of the hazard service.
Worked example: a sea breeze at a coastal aerodrome typically peaks mid-afternoon, veering the wind onshore and lowering temperature; a night katabatic flow down a valley can produce a low-level wind shear on approach.
Trap: the subtropical high is a subsidence region, not a region of rising air; it produces clear skies and deserts, not cloud.